objtool: Add tool to perform compile-time stack metadata validation

This adds a host tool named objtool which has a "check" subcommand which
analyzes .o files to ensure the validity of stack metadata.  It enforces
a set of rules on asm code and C inline assembly code so that stack
traces can be reliable.

For each function, it recursively follows all possible code paths and
validates the correct frame pointer state at each instruction.

It also follows code paths involving kernel special sections, like
.altinstructions, __jump_table, and __ex_table, which can add
alternative execution paths to a given instruction (or set of
instructions).  Similarly, it knows how to follow switch statements, for
which gcc sometimes uses jump tables.

Here are some of the benefits of validating stack metadata:

a) More reliable stack traces for frame pointer enabled kernels

   Frame pointers are used for debugging purposes.  They allow runtime
   code and debug tools to be able to walk the stack to determine the
   chain of function call sites that led to the currently executing
   code.

   For some architectures, frame pointers are enabled by
   CONFIG_FRAME_POINTER.  For some other architectures they may be
   required by the ABI (sometimes referred to as "backchain pointers").

   For C code, gcc automatically generates instructions for setting up
   frame pointers when the -fno-omit-frame-pointer option is used.

   But for asm code, the frame setup instructions have to be written by
   hand, which most people don't do.  So the end result is that
   CONFIG_FRAME_POINTER is honored for C code but not for most asm code.

   For stack traces based on frame pointers to be reliable, all
   functions which call other functions must first create a stack frame
   and update the frame pointer.  If a first function doesn't properly
   create a stack frame before calling a second function, the *caller*
   of the first function will be skipped on the stack trace.

   For example, consider the following example backtrace with frame
   pointers enabled:

     [<ffffffff81812584>] dump_stack+0x4b/0x63
     [<ffffffff812d6dc2>] cmdline_proc_show+0x12/0x30
     [<ffffffff8127f568>] seq_read+0x108/0x3e0
     [<ffffffff812cce62>] proc_reg_read+0x42/0x70
     [<ffffffff81256197>] __vfs_read+0x37/0x100
     [<ffffffff81256b16>] vfs_read+0x86/0x130
     [<ffffffff81257898>] SyS_read+0x58/0xd0
     [<ffffffff8181c1f2>] entry_SYSCALL_64_fastpath+0x12/0x76

   It correctly shows that the caller of cmdline_proc_show() is
   seq_read().

   If we remove the frame pointer logic from cmdline_proc_show() by
   replacing the frame pointer related instructions with nops, here's
   what it looks like instead:

     [<ffffffff81812584>] dump_stack+0x4b/0x63
     [<ffffffff812d6dc2>] cmdline_proc_show+0x12/0x30
     [<ffffffff812cce62>] proc_reg_read+0x42/0x70
     [<ffffffff81256197>] __vfs_read+0x37/0x100
     [<ffffffff81256b16>] vfs_read+0x86/0x130
     [<ffffffff81257898>] SyS_read+0x58/0xd0
     [<ffffffff8181c1f2>] entry_SYSCALL_64_fastpath+0x12/0x76

   Notice that cmdline_proc_show()'s caller, seq_read(), has been
   skipped.  Instead the stack trace seems to show that
   cmdline_proc_show() was called by proc_reg_read().

   The benefit of "objtool check" here is that because it ensures that
   *all* functions honor CONFIG_FRAME_POINTER, no functions will ever[*]
   be skipped on a stack trace.

   [*] unless an interrupt or exception has occurred at the very
       beginning of a function before the stack frame has been created,
       or at the very end of the function after the stack frame has been
       destroyed.  This is an inherent limitation of frame pointers.

b) 100% reliable stack traces for DWARF enabled kernels

   This is not yet implemented.  For more details about what is planned,
   see tools/objtool/Documentation/stack-validation.txt.

c) Higher live patching compatibility rate

   This is not yet implemented.  For more details about what is planned,
   see tools/objtool/Documentation/stack-validation.txt.

To achieve the validation, "objtool check" enforces the following rules:

1. Each callable function must be annotated as such with the ELF
   function type.  In asm code, this is typically done using the
   ENTRY/ENDPROC macros.  If objtool finds a return instruction
   outside of a function, it flags an error since that usually indicates
   callable code which should be annotated accordingly.

   This rule is needed so that objtool can properly identify each
   callable function in order to analyze its stack metadata.

2. Conversely, each section of code which is *not* callable should *not*
   be annotated as an ELF function.  The ENDPROC macro shouldn't be used
   in this case.

   This rule is needed so that objtool can ignore non-callable code.
   Such code doesn't have to follow any of the other rules.

3. Each callable function which calls another function must have the
   correct frame pointer logic, if required by CONFIG_FRAME_POINTER or
   the architecture's back chain rules.  This can by done in asm code
   with the FRAME_BEGIN/FRAME_END macros.

   This rule ensures that frame pointer based stack traces will work as
   designed.  If function A doesn't create a stack frame before calling
   function B, the _caller_ of function A will be skipped on the stack
   trace.

4. Dynamic jumps and jumps to undefined symbols are only allowed if:

   a) the jump is part of a switch statement; or

   b) the jump matches sibling call semantics and the frame pointer has
      the same value it had on function entry.

   This rule is needed so that objtool can reliably analyze all of a
   function's code paths.  If a function jumps to code in another file,
   and it's not a sibling call, objtool has no way to follow the jump
   because it only analyzes a single file at a time.

5. A callable function may not execute kernel entry/exit instructions.
   The only code which needs such instructions is kernel entry code,
   which shouldn't be be in callable functions anyway.

   This rule is just a sanity check to ensure that callable functions
   return normally.

It currently only supports x86_64.  I tried to make the code generic so
that support for other architectures can hopefully be plugged in
relatively easily.

On my Lenovo laptop with a i7-4810MQ 4-core/8-thread CPU, building the
kernel with objtool checking every .o file adds about three seconds of
total build time.  It hasn't been optimized for performance yet, so
there are probably some opportunities for better build performance.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Bernd Petrovitsch <bernd@petrovitsch.priv.at>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Chris J Arges <chris.j.arges@canonical.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michal Marek <mmarek@suse.cz>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Pedro Alves <palves@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/f3efb173de43bd067b060de73f856567c0fa1174.1456719558.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 594 insertions, 0 deletions

diff --git a/tools/objtool/arch/x86/insn/insn.c b/tools/objtool/arch/x86/insn/insn.c
new file mode 100644
index 000000000000..47314a64399c
--- /dev/null
+++ b/tools/objtool/arch/x86/insn/insn.c
@@ -0,0 +1,594 @@
+/*
+ * x86 instruction analysis
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
+ *
+ * Copyright (C) IBM Corporation, 2002, 2004, 2009
+ */
+
+#ifdef __KERNEL__
+#include <linux/string.h>
+#else
+#include <string.h>
+#endif
+#include "inat.h"
+#include "insn.h"
+
+/* Verify next sizeof(t) bytes can be on the same instruction */
+#define validate_next(t, insn, n)	\
+	((insn)->next_byte + sizeof(t) + n <= (insn)->end_kaddr)
+
+#define __get_next(t, insn)	\
+	({ t r = *(t*)insn->next_byte; insn->next_byte += sizeof(t); r; })
+
+#define __peek_nbyte_next(t, insn, n)	\
+	({ t r = *(t*)((insn)->next_byte + n); r; })
+
+#define get_next(t, insn)	\
+	({ if (unlikely(!validate_next(t, insn, 0))) goto err_out; __get_next(t, insn); })
+
+#define peek_nbyte_next(t, insn, n)	\
+	({ if (unlikely(!validate_next(t, insn, n))) goto err_out; __peek_nbyte_next(t, insn, n); })
+
+#define peek_next(t, insn)	peek_nbyte_next(t, insn, 0)
+
+/**
+ * insn_init() - initialize struct insn
+ * @insn:	&struct insn to be initialized
+ * @kaddr:	address (in kernel memory) of instruction (or copy thereof)
+ * @x86_64:	!0 for 64-bit kernel or 64-bit app
+ */
+void insn_init(struct insn *insn, const void *kaddr, int buf_len, int x86_64)
+{
+	/*
+	 * Instructions longer than MAX_INSN_SIZE (15 bytes) are invalid
+	 * even if the input buffer is long enough to hold them.
+	 */
+	if (buf_len > MAX_INSN_SIZE)
+		buf_len = MAX_INSN_SIZE;
+
+	memset(insn, 0, sizeof(*insn));
+	insn->kaddr = kaddr;
+	insn->end_kaddr = kaddr + buf_len;
+	insn->next_byte = kaddr;
+	insn->x86_64 = x86_64 ? 1 : 0;
+	insn->opnd_bytes = 4;
+	if (x86_64)
+		insn->addr_bytes = 8;
+	else
+		insn->addr_bytes = 4;
+}
+
+/**
+ * insn_get_prefixes - scan x86 instruction prefix bytes
+ * @insn:	&struct insn containing instruction
+ *
+ * Populates the @insn->prefixes bitmap, and updates @insn->next_byte
+ * to point to the (first) opcode.  No effect if @insn->prefixes.got
+ * is already set.
+ */
+void insn_get_prefixes(struct insn *insn)
+{
+	struct insn_field *prefixes = &insn->prefixes;
+	insn_attr_t attr;
+	insn_byte_t b, lb;
+	int i, nb;
+
+	if (prefixes->got)
+		return;
+
+	nb = 0;
+	lb = 0;
+	b = peek_next(insn_byte_t, insn);
+	attr = inat_get_opcode_attribute(b);
+	while (inat_is_legacy_prefix(attr)) {
+		/* Skip if same prefix */
+		for (i = 0; i < nb; i++)
+			if (prefixes->bytes[i] == b)
+				goto found;
+		if (nb == 4)
+			/* Invalid instruction */
+			break;
+		prefixes->bytes[nb++] = b;
+		if (inat_is_address_size_prefix(attr)) {
+			/* address size switches 2/4 or 4/8 */
+			if (insn->x86_64)
+				insn->addr_bytes ^= 12;
+			else
+				insn->addr_bytes ^= 6;
+		} else if (inat_is_operand_size_prefix(attr)) {
+			/* oprand size switches 2/4 */
+			insn->opnd_bytes ^= 6;
+		}
+found:
+		prefixes->nbytes++;
+		insn->next_byte++;
+		lb = b;
+		b = peek_next(insn_byte_t, insn);
+		attr = inat_get_opcode_attribute(b);
+	}
+	/* Set the last prefix */
+	if (lb && lb != insn->prefixes.bytes[3]) {
+		if (unlikely(insn->prefixes.bytes[3])) {
+			/* Swap the last prefix */
+			b = insn->prefixes.bytes[3];
+			for (i = 0; i < nb; i++)
+				if (prefixes->bytes[i] == lb)
+					prefixes->bytes[i] = b;
+		}
+		insn->prefixes.bytes[3] = lb;
+	}
+
+	/* Decode REX prefix */
+	if (insn->x86_64) {
+		b = peek_next(insn_byte_t, insn);
+		attr = inat_get_opcode_attribute(b);
+		if (inat_is_rex_prefix(attr)) {
+			insn->rex_prefix.value = b;
+			insn->rex_prefix.nbytes = 1;
+			insn->next_byte++;
+			if (X86_REX_W(b))
+				/* REX.W overrides opnd_size */
+				insn->opnd_bytes = 8;
+		}
+	}
+	insn->rex_prefix.got = 1;
+
+	/* Decode VEX prefix */
+	b = peek_next(insn_byte_t, insn);
+	attr = inat_get_opcode_attribute(b);
+	if (inat_is_vex_prefix(attr)) {
+		insn_byte_t b2 = peek_nbyte_next(insn_byte_t, insn, 1);
+		if (!insn->x86_64) {
+			/*
+			 * In 32-bits mode, if the [7:6] bits (mod bits of
+			 * ModRM) on the second byte are not 11b, it is
+			 * LDS or LES.
+			 */
+			if (X86_MODRM_MOD(b2) != 3)
+				goto vex_end;
+		}
+		insn->vex_prefix.bytes[0] = b;
+		insn->vex_prefix.bytes[1] = b2;
+		if (inat_is_vex3_prefix(attr)) {
+			b2 = peek_nbyte_next(insn_byte_t, insn, 2);
+			insn->vex_prefix.bytes[2] = b2;
+			insn->vex_prefix.nbytes = 3;
+			insn->next_byte += 3;
+			if (insn->x86_64 && X86_VEX_W(b2))
+				/* VEX.W overrides opnd_size */
+				insn->opnd_bytes = 8;
+		} else {
+			/*
+			 * For VEX2, fake VEX3-like byte#2.
+			 * Makes it easier to decode vex.W, vex.vvvv,
+			 * vex.L and vex.pp. Masking with 0x7f sets vex.W == 0.
+			 */
+			insn->vex_prefix.bytes[2] = b2 & 0x7f;
+			insn->vex_prefix.nbytes = 2;
+			insn->next_byte += 2;
+		}
+	}
+vex_end:
+	insn->vex_prefix.got = 1;
+
+	prefixes->got = 1;
+
+err_out:
+	return;
+}
+
+/**
+ * insn_get_opcode - collect opcode(s)
+ * @insn:	&struct insn containing instruction
+ *
+ * Populates @insn->opcode, updates @insn->next_byte to point past the
+ * opcode byte(s), and set @insn->attr (except for groups).
+ * If necessary, first collects any preceding (prefix) bytes.
+ * Sets @insn->opcode.value = opcode1.  No effect if @insn->opcode.got
+ * is already 1.
+ */
+void insn_get_opcode(struct insn *insn)
+{
+	struct insn_field *opcode = &insn->opcode;
+	insn_byte_t op;
+	int pfx_id;
+	if (opcode->got)
+		return;
+	if (!insn->prefixes.got)
+		insn_get_prefixes(insn);
+
+	/* Get first opcode */
+	op = get_next(insn_byte_t, insn);
+	opcode->bytes[0] = op;
+	opcode->nbytes = 1;
+
+	/* Check if there is VEX prefix or not */
+	if (insn_is_avx(insn)) {
+		insn_byte_t m, p;
+		m = insn_vex_m_bits(insn);
+		p = insn_vex_p_bits(insn);
+		insn->attr = inat_get_avx_attribute(op, m, p);
+		if (!inat_accept_vex(insn->attr) && !inat_is_group(insn->attr))
+			insn->attr = 0;	/* This instruction is bad */
+		goto end;	/* VEX has only 1 byte for opcode */
+	}
+
+	insn->attr = inat_get_opcode_attribute(op);
+	while (inat_is_escape(insn->attr)) {
+		/* Get escaped opcode */
+		op = get_next(insn_byte_t, insn);
+		opcode->bytes[opcode->nbytes++] = op;
+		pfx_id = insn_last_prefix_id(insn);
+		insn->attr = inat_get_escape_attribute(op, pfx_id, insn->attr);
+	}
+	if (inat_must_vex(insn->attr))
+		insn->attr = 0;	/* This instruction is bad */
+end:
+	opcode->got = 1;
+
+err_out:
+	return;
+}
+
+/**
+ * insn_get_modrm - collect ModRM byte, if any
+ * @insn:	&struct insn containing instruction
+ *
+ * Populates @insn->modrm and updates @insn->next_byte to point past the
+ * ModRM byte, if any.  If necessary, first collects the preceding bytes
+ * (prefixes and opcode(s)).  No effect if @insn->modrm.got is already 1.
+ */
+void insn_get_modrm(struct insn *insn)
+{
+	struct insn_field *modrm = &insn->modrm;
+	insn_byte_t pfx_id, mod;
+	if (modrm->got)
+		return;
+	if (!insn->opcode.got)
+		insn_get_opcode(insn);
+
+	if (inat_has_modrm(insn->attr)) {
+		mod = get_next(insn_byte_t, insn);
+		modrm->value = mod;
+		modrm->nbytes = 1;
+		if (inat_is_group(insn->attr)) {
+			pfx_id = insn_last_prefix_id(insn);
+			insn->attr = inat_get_group_attribute(mod, pfx_id,
+							      insn->attr);
+			if (insn_is_avx(insn) && !inat_accept_vex(insn->attr))
+				insn->attr = 0;	/* This is bad */
+		}
+	}
+
+	if (insn->x86_64 && inat_is_force64(insn->attr))
+		insn->opnd_bytes = 8;
+	modrm->got = 1;
+
+err_out:
+	return;
+}
+
+
+/**
+ * insn_rip_relative() - Does instruction use RIP-relative addressing mode?
+ * @insn:	&struct insn containing instruction
+ *
+ * If necessary, first collects the instruction up to and including the
+ * ModRM byte.  No effect if @insn->x86_64 is 0.
+ */
+int insn_rip_relative(struct insn *insn)
+{
+	struct insn_field *modrm = &insn->modrm;
+
+	if (!insn->x86_64)
+		return 0;
+	if (!modrm->got)
+		insn_get_modrm(insn);
+	/*
+	 * For rip-relative instructions, the mod field (top 2 bits)
+	 * is zero and the r/m field (bottom 3 bits) is 0x5.
+	 */
+	return (modrm->nbytes && (modrm->value & 0xc7) == 0x5);
+}
+
+/**
+ * insn_get_sib() - Get the SIB byte of instruction
+ * @insn:	&struct insn containing instruction
+ *
+ * If necessary, first collects the instruction up to and including the
+ * ModRM byte.
+ */
+void insn_get_sib(struct insn *insn)
+{
+	insn_byte_t modrm;
+
+	if (insn->sib.got)
+		return;
+	if (!insn->modrm.got)
+		insn_get_modrm(insn);
+	if (insn->modrm.nbytes) {
+		modrm = (insn_byte_t)insn->modrm.value;
+		if (insn->addr_bytes != 2 &&
+		    X86_MODRM_MOD(modrm) != 3 && X86_MODRM_RM(modrm) == 4) {
+			insn->sib.value = get_next(insn_byte_t, insn);
+			insn->sib.nbytes = 1;
+		}
+	}
+	insn->sib.got = 1;
+
+err_out:
+	return;
+}
+
+
+/**
+ * insn_get_displacement() - Get the displacement of instruction
+ * @insn:	&struct insn containing instruction
+ *
+ * If necessary, first collects the instruction up to and including the
+ * SIB byte.
+ * Displacement value is sign-expanded.
+ */
+void insn_get_displacement(struct insn *insn)
+{
+	insn_byte_t mod, rm, base;
+
+	if (insn->displacement.got)
+		return;
+	if (!insn->sib.got)
+		insn_get_sib(insn);
+	if (insn->modrm.nbytes) {
+		/*
+		 * Interpreting the modrm byte:
+		 * mod = 00 - no displacement fields (exceptions below)
+		 * mod = 01 - 1-byte displacement field
+		 * mod = 10 - displacement field is 4 bytes, or 2 bytes if
+		 * 	address size = 2 (0x67 prefix in 32-bit mode)
+		 * mod = 11 - no memory operand
+		 *
+		 * If address size = 2...
+		 * mod = 00, r/m = 110 - displacement field is 2 bytes
+		 *
+		 * If address size != 2...
+		 * mod != 11, r/m = 100 - SIB byte exists
+		 * mod = 00, SIB base = 101 - displacement field is 4 bytes
+		 * mod = 00, r/m = 101 - rip-relative addressing, displacement
+		 * 	field is 4 bytes
+		 */
+		mod = X86_MODRM_MOD(insn->modrm.value);
+		rm = X86_MODRM_RM(insn->modrm.value);
+		base = X86_SIB_BASE(insn->sib.value);
+		if (mod == 3)
+			goto out;
+		if (mod == 1) {
+			insn->displacement.value = get_next(char, insn);
+			insn->displacement.nbytes = 1;
+		} else if (insn->addr_bytes == 2) {
+			if ((mod == 0 && rm == 6) || mod == 2) {
+				insn->displacement.value =
+					 get_next(short, insn);
+				insn->displacement.nbytes = 2;
+			}
+		} else {
+			if ((mod == 0 && rm == 5) || mod == 2 ||
+			    (mod == 0 && base == 5)) {
+				insn->displacement.value = get_next(int, insn);
+				insn->displacement.nbytes = 4;
+			}
+		}
+	}
+out:
+	insn->displacement.got = 1;
+
+err_out:
+	return;
+}
+
+/* Decode moffset16/32/64. Return 0 if failed */
+static int __get_moffset(struct insn *insn)
+{
+	switch (insn->addr_bytes) {
+	case 2:
+		insn->moffset1.value = get_next(short, insn);
+		insn->moffset1.nbytes = 2;
+		break;
+	case 4:
+		insn->moffset1.value = get_next(int, insn);
+		insn->moffset1.nbytes = 4;
+		break;
+	case 8:
+		insn->moffset1.value = get_next(int, insn);
+		insn->moffset1.nbytes = 4;
+		insn->moffset2.value = get_next(int, insn);
+		insn->moffset2.nbytes = 4;
+		break;
+	default:	/* opnd_bytes must be modified manually */
+		goto err_out;
+	}
+	insn->moffset1.got = insn->moffset2.got = 1;
+
+	return 1;
+
+err_out:
+	return 0;
+}
+
+/* Decode imm v32(Iz). Return 0 if failed */
+static int __get_immv32(struct insn *insn)
+{
+	switch (insn->opnd_bytes) {
+	case 2:
+		insn->immediate.value = get_next(short, insn);
+		insn->immediate.nbytes = 2;
+		break;
+	case 4:
+	case 8:
+		insn->immediate.value = get_next(int, insn);
+		insn->immediate.nbytes = 4;
+		break;
+	default:	/* opnd_bytes must be modified manually */
+		goto err_out;
+	}
+
+	return 1;
+
+err_out:
+	return 0;
+}
+
+/* Decode imm v64(Iv/Ov), Return 0 if failed */
+static int __get_immv(struct insn *insn)
+{
+	switch (insn->opnd_bytes) {
+	case 2:
+		insn->immediate1.value = get_next(short, insn);
+		insn->immediate1.nbytes = 2;
+		break;
+	case 4:
+		insn->immediate1.value = get_next(int, insn);
+		insn->immediate1.nbytes = 4;
+		break;
+	case 8:
+		insn->immediate1.value = get_next(int, insn);
+		insn->immediate1.nbytes = 4;
+		insn->immediate2.value = get_next(int, insn);
+		insn->immediate2.nbytes = 4;
+		break;
+	default:	/* opnd_bytes must be modified manually */
+		goto err_out;
+	}
+	insn->immediate1.got = insn->immediate2.got = 1;
+
+	return 1;
+err_out:
+	return 0;
+}
+
+/* Decode ptr16:16/32(Ap) */
+static int __get_immptr(struct insn *insn)
+{
+	switch (insn->opnd_bytes) {
+	case 2:
+		insn->immediate1.value = get_next(short, insn);
+		insn->immediate1.nbytes = 2;
+		break;
+	case 4:
+		insn->immediate1.value = get_next(int, insn);
+		insn->immediate1.nbytes = 4;
+		break;
+	case 8:
+		/* ptr16:64 is not exist (no segment) */
+		return 0;
+	default:	/* opnd_bytes must be modified manually */
+		goto err_out;
+	}
+	insn->immediate2.value = get_next(unsigned short, insn);
+	insn->immediate2.nbytes = 2;
+	insn->immediate1.got = insn->immediate2.got = 1;
+
+	return 1;
+err_out:
+	return 0;
+}
+
+/**
+ * insn_get_immediate() - Get the immediates of instruction
+ * @insn:	&struct insn containing instruction
+ *
+ * If necessary, first collects the instruction up to and including the
+ * displacement bytes.
+ * Basically, most of immediates are sign-expanded. Unsigned-value can be
+ * get by bit masking with ((1 << (nbytes * 8)) - 1)
+ */
+void insn_get_immediate(struct insn *insn)
+{
+	if (insn->immediate.got)
+		return;
+	if (!insn->displacement.got)
+		insn_get_displacement(insn);
+
+	if (inat_has_moffset(insn->attr)) {
+		if (!__get_moffset(insn))
+			goto err_out;
+		goto done;
+	}
+
+	if (!inat_has_immediate(insn->attr))
+		/* no immediates */
+		goto done;
+
+	switch (inat_immediate_size(insn->attr)) {
+	case INAT_IMM_BYTE:
+		insn->immediate.value = get_next(char, insn);
+		insn->immediate.nbytes = 1;
+		break;
+	case INAT_IMM_WORD:
+		insn->immediate.value = get_next(short, insn);
+		insn->immediate.nbytes = 2;
+		break;
+	case INAT_IMM_DWORD:
+		insn->immediate.value = get_next(int, insn);
+		insn->immediate.nbytes = 4;
+		break;
+	case INAT_IMM_QWORD:
+		insn->immediate1.value = get_next(int, insn);
+		insn->immediate1.nbytes = 4;
+		insn->immediate2.value = get_next(int, insn);
+		insn->immediate2.nbytes = 4;
+		break;
+	case INAT_IMM_PTR:
+		if (!__get_immptr(insn))
+			goto err_out;
+		break;
+	case INAT_IMM_VWORD32:
+		if (!__get_immv32(insn))
+			goto err_out;
+		break;
+	case INAT_IMM_VWORD:
+		if (!__get_immv(insn))
+			goto err_out;
+		break;
+	default:
+		/* Here, insn must have an immediate, but failed */
+		goto err_out;
+	}
+	if (inat_has_second_immediate(insn->attr)) {
+		insn->immediate2.value = get_next(char, insn);
+		insn->immediate2.nbytes = 1;
+	}
+done:
+	insn->immediate.got = 1;
+
+err_out:
+	return;
+}
+
+/**
+ * insn_get_length() - Get the length of instruction
+ * @insn:	&struct insn containing instruction
+ *
+ * If necessary, first collects the instruction up to and including the
+ * immediates bytes.
+ */
+void insn_get_length(struct insn *insn)
+{
+	if (insn->length)
+		return;
+	if (!insn->immediate.got)
+		insn_get_immediate(insn);
+	insn->length = (unsigned char)((unsigned long)insn->next_byte
+				     - (unsigned long)insn->kaddr);
+}